An acrylic acid-based polymer such as sodium polyacrylate is an industrially important compound which is used for wide applications including a pigment dispersant, a builder for detergent, or an inorganic precipitation inhibitor. For these applications, an acrylic acid-based polymer having a low molecular weight like a weight average molecular weight of about 1,000 to 30,000 is preferred, and the molecular weight distribution, which is expressed as a ratio (Mw/Mn) obtained by dividing a weight average molecular weight (Mw) by a number average molecular weight (Mn), that is, variation, is preferably as narrow as possible.
Further, in terms of production thereof, a method with good efficiency such as shortened reaction time or improved productivity is obviously preferred. For a suitable method, development of a continuous production method is also under progress in addition to a production method of a related art which is based on a batch mode.
Under the circumstances, several methods have been suggested with regard to a production method of an acrylic acid-based polymer having a low molecular weight.
Patent Document 1 discloses a novel cotelomer compound useful for inhibition of precipitation of scales from corrosion of a metal and/or an aqueous system and/or promotion of dispersion of particles in an aqueous system, and a production method therefor.
Additionally, the applicant suggests a production method of an acrylic acid-based polymer having a low molecular weight and a narrow molecular weight distribution using a continuous reaction device consisting of plural reactors in which at least one reactor is a tank type reactor in Patent Documents 2 and 3.
Patent Documents 4 and 5 describe that an acrylic acid-based polymer having a low molecular weight and also a narrow molecular weight distribution can be effectively obtained by stirring a reaction liquid with power consumption for stirring (Pv) of 0.5 kW/m3 or higher.
Further, Patent Document 6 discloses a continuous production method for obtaining with high efficiency a water soluble copolymer having a narrow molecular weight distribution in which a reaction device having a tank and a circulation line consisting of pipes which circulate the outside of the tank is used.